[0001] The prior art relating to filters for the extraction of dusts from gases comprises
sack filters essentially constituted by a container enclosing a battery of sacks made
of a filtering material, which sacks are arranged reciprocally parallel and are mounted
on a square support plate which doubles as a lid for the container. The edge describing
the mouth of each sack is fixed to a frame in turn fixed to the support plate. The
plate exhibits a plurality of longitudinal parallel apertures to each of which a frame
of a single sack is fixed. Further, a rigid net structure is usually arranged internally
of each sack to prevent the walls thereof from coming into reciprocal contact without
for that obstucting in any way the passage of the filtered gas.
[0002] This gas (dusty air, smoke etc.) is introduced into the container and, after filtering,
exits from the sack mouths; the filtered detritus is collected at the bottom of the
container.
[0003] Known-type sack filters of the above-described type present, however, some drawbacks.
[0004] A first of these is that the available filtering surface, in relation to the overall
filter mass, has an upper limit which depends on constructional factors, as the support
plate can only bear a certain quite small number of frames, and therefore only a similarly
limited number of sacks.
[0005] Secondly, known-type filters are constructively complex, expensive and laborious
to manufacture.
[0006] The main aim of the present invention is to obviate the above-mentioned limits and
drawbacks in the prior art by providing a sack filter, constructionally simple and
economical, which is provided with an air-contact surface per unit of volume which
is larger than that of existing filters.
[0007] Some advantages of the present invention are its compactness, its simplicity of manufacture
and installation, the fact that sacks can be fitted very closely ranked in relation
to the size of the support plate therefor, the fact that a single sack can be closed
(when worn or broken) without significantly compromising the total delivery rate and
functionability of the filter.
[0008] The invention also advantageously enables the sacks to be mounted on the support
plate at a reciprocal distance which is the minimum distance below which free air
passage would not be possible between one sack and a next; below such limit the density
of sacks would cause a drastic reduction in the volume of air filtered.
[0009] These aims and others besides are all attained by the filter of the invention, as
it is characterized in the claims that follow.
[0010] Further characteristics and advantages of the present invention will better emerge
from the detailed description that follows, of an embodiment of the invention, illustrated
in the form of a non-limiting example in the accompanying drawings, in which:
figure 1 shows an exploded schematic perspective view of the filter;
figure 2 shows a schematic frontal view of the sack support plate;
figure 3 is a section made according to line III-III of figure 2.
[0011] With reference to the figures of the drawings, 1 denotes in its entirety a sack filter,
comprising a rectangular support plate 2, on which surface a plurality of parallel
narrow and elongate apertures 3 are afforded. The support plate 2 is made of a plastic
material which is stably solid in atmospheric conditions, for example polyeurethane.
The filter 1 comprises a plurality of sacks 4, flat and reciprocally parallel, each
associated to an aperture 3, each having a mouth 5 facing said aperture 3 and being
made of a filtering material.
[0012] The edge 6 of the mouth 5 of each sack 4 is embedded in the material of the support
plate 2 at a perimeter zone of a respective aperture 3, such that the sack 4 is solidly
anchored to the support plate 2. The support plate 2 and the sacks 4 thus form a single
piece which can be manufactured extremely simply in comparison to sack filters of
known type, for example by moulding or casting of the plastic material.
[0013] To obtain a better anchoring of the sacks to the support plate 2, as well as to prevent
lacerations of the apertures 3 in proximity of the anchoring zone, the embedded edge
6 is preferably perpendicular to the support plate 2 and parallel to the walls describing
the relative aperture 3 on the support plate 2. The depth to which the edge 6 is embedded,
measured normally to the walls of the aperture 3, is about the same as the breadth
of the filtering cloth of the sack 4.
[0014] The embedding of the edges 6 of the mouths 5 of the sacks 4 into the plastic is realized,
for example, by means of insertion of said edges 6 into the moulding cavity of the
die for the support plate 2, before molten plastic is introduced into the die. After
solidification of the plastic material, the sacks 4 are solidly anchored to the support
plate 2 material. To enhance the anchoring between the material of the support plate
2 and the edges 6 of the sacks 4, the sacks 4 exhibit projections 7, constituted for
example by metal bosses solidly fixed to the material of the sacks 4. To improve still
more the anchoring of the sacks to the plastic material, once the support plate 2
has solidified, further fixing means, such as metal clips, can be applied.
[0015] The rectangular support plate 2 is mounted on a container 8 provided with an inlet
9. The support plate 2 functions as a lid for the container 8.
[0016] The battery of sacks 4, when the support plate 2 is mounted on the container 8, is
contained internally of the container 8. A rigid net structure 10 is arranged internally
of each sack 4 to prevent the walls of the sack 4 from reciprocally contacting, without
at the same time obstructing the passage of the filtered air. Also arranged internally
of the sack 4 are means 11 for keeping the sacks 4 stretched and elongate, which means
11 are operatively associated with the ends of the sacks 4 opposite to the mouths
5 thereof.
[0017] The filter 1 further comprises a plurality of lids 12, which can be used to close
one or more of the apertures 3 when necessary.
[0018] During functioning, the gas to be filtered (smoke, dusty air etc.) is introduced
internally of the container 8 through the inlet 9, and exits, after filtering, through
the mouths 5 of the sacks 4.
[0019] Thanks to the single unified structure formed by the support plate 2 and the battery
of sacks 4, a high number of sacks 4 can be mounted on the support plate 2, so that
a large filtering surface is obtained in relation to the total volume of the filter
1.
[0020] Obviously it is still necessary to leave a free space between one sack 4 and another
sufficient to allow passage of the air to be filtered. It is, however, also true that
with the present invention this minimum free space no longer depends on constructional
reasons deriving from the considerable lateral mass of the frames used up to the present
day for supporting the single sacks, but only on the space necessary for the free
passage of the air. The frames previously used do not in fact figure in the present
invention: indeed, it can be stated that one of the most important advantages of the
present invention is the fact that with respect to the prior art the filter frame
is not present, its sack-supporting role having been obviated by the fact of embedding
a portion of the sacks in the plastic material of which the support plate 2 is made
- a fact which also enormously simplifies manufacture of the filter.
[0021] Given the high number of filtering sacks 4, in cases of breakage or wear of one or
more sacks 4, it is possible to deactivate such sacks 4 by closing the relative apertures
3 with the lids 12, without causing a resulting significant loss of total potential
of the filter.
1. A sack filter, comprising: a support plate (2) on a surface of which a plurality of
apertures (3) is arranged; a plurality of sacks (4), each of which is associated to
an aperture (3) of the plurality of apertures (3), which sacks (4) are made of a filtering
cloth and each of which sacks (4) is provided with a mouth (5) disposed in a position
facing said aperture (3); characterized in that an edge (6) of said mouth (5) of each
of said sacks (4) is embedded in a material of which said support plate (2) is made,
at a perimeter zone of the aperture (3), such that said sacks (4) are solidly anchored
to said support plate (2).
2. A filter as in claim 1, characterized in that said support plate (2) is realized in
a plastic material which is stably solid in atmospheric conditions.
3. A filter as in claims 1 or 2, characterized in that the edge (6) of the mouth (5)
of each of the sacks (4), which edge (6) is embedded in the material of said support
plate (2), is provided with projections (7) for enhancing an anchoring between said
edge (6) and the plastic material of the support plate (2).
4. A filter as in any one of the preceding claims, characterized in that it comprises
a plurality of lids (12) conformed in such a way as to close one or more of said apertures
(3) should this be required.
5. A filter as in any one of the preceding claims, characterized in that the edge (6)
of the mouth (5) of each sack (4), which is embedded in the material of the support
plate (2), is perpendicular to the support plate (2) and parallel to the walls describing
the apertures (3) on the support plate (2).
6. A filter as in claim 5, characterized in that a depth to which said edge (6) is embedded
in said support plate (2), measured in a normal direction to said walls describing
said apertures (3), is of about a same measurement as a breadth of a filtering surface
of said sack (4).